Chair backrest



FIG. 1 is a perspective view of the chair backrest showing my new design;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a left side elevation view thereof;

FIG. 5 is a right side elevation view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken line showing of screws is for the purpose of illustrating portions of the chair backrest and forms no part of the claimed design. 

CLAIM The ornamental design for a chair backrest, as shown and described. 